Fast wave transmission line coupled to a plasma



pri W, w68 l.. s. NAPOLI ETAL FAST WAVE TRANSMISSION LINE COUPLED TO A PLASMA 3 sheets-sneer 1 Filed Jan. 2, 1964 April 16, 1968 L.. s. NAPOLI ETAL 3,378,723

FAST WAVE TRANSMISSION LINE COUPLED'TO A PLASMA File Jan. E, 1964 3 Sheets--Sheef I;

BY i gw l April 15, 1968 L.. s. NAPOLI ETAL 3,378,723

FAST WAVE TRANSMISSION LINE COUPLED TO A PLASMA Filed Jan. 2, 1964 3 Sheets-b`heet ...a ...III

JNVENTOR5 A /az//f I /Waz/ United States Patent O 3,378,723 FAST WAVE TRANSMISSION LINE COUPLED TO A PLASMA Louis S. Napoli, Hamilton Square, and George A. Swartz,

Princeton Junction, NJ., assignors to Radio Corporation of America, a corporation of Delaware Filed Jan. 2, 1964, Ser. No. 335,139

Claims. (Cl. 315-39) The present invention relates to plasma coupling means, and particularly to means for coupling a fast wave transmission line to the plasma in a plasma tube, such as a beam-plasma interaction tube.

A beam-plasma interaction tube is an electron tube in which an electron beam or stream is projected through a plasma region for interaction with the plasma to amplify or generate an RF signal. In an amplifier, the RF signal is coupled to and modulates the beam prior to injection thereof into the plasma. In an oscillator, the RF signal is generated by the beam-plasma interaction. The ampliiier requires both input and output coupling means, whereas the oscillator requires only an output coupling means. Thus, a beam-plasma interaction tube requires:

(l) Means for generating a plasma, or neutral mixture of charged particles;

(2) Means for generating and projecting a stream of electrons through the plasma; and

(3) Means for coupling the electron stream to at least one fast wave RF transmission line, such as a waveguide or coaxial line.

Beam-plasma interaction normally occurs at or near the plasma frequency fp of the electrons in the plasma. fp is a function of the electron density n as follows:

where e and m are the charge and mass, respectively, of the electron. The angular plasma frequency wp is equal to Zit-fp. For example, operation at a signal frequency of 300 kmc., or 1 mm., wavelength, requires an electron density just above 1015 electrons per cm. Since the beamplasma interaction tube does not involve any periodic structures in the interaction region, the operating lfrequency, and power output are limited only by the available electron density.

The input and output coupling heretofore used in beamplasma tubes have necessarily been slow-wave structures or klystron type gap structures, which are limited in their power capabilities, especially at very high frequencies. Some of the limitations of such structures are:

(1) The diameter of the slow-wave structure is limited to about a wavelength because of moding difficulties;

(2) For a given dimension the power output is limited by the ability of the structure to `dissipate the heat produced by beam interception and RF heating;

(3) The voltages on the structure are limited by breakdown and multipactor effects;

(4) High power output is often incompatible with bandwidth requirements because of the dispersion of the RF structure;

(5) The RF losses increase with frequency; and

(6) Gap structures are inherently narrow band with coupled cavity resonators and very inefficient without resonators.

An object of the present invention is to provide improved means for coupling a fast wave transmission line to a plasma.

A further object is to provide improved means for coupling an electron stream in an electron tube to a fast wave input or output transmission line.

Another object is to provide means utilizing the plasma ice in a beam-plasma interaction tube to couple a fast wave transmission to the beam, and vice-versa.

A further object is to provide an improved beam-plasma interaction tube.

These and other objects are accomplished in accordance with the present invention by producing a plasma in a given region, coupling a fast wave input signal transmission line to the plasma in a first portion of the region to excite a fast wave on the plasma at the signal frequency for propagation to a second portion of the region, projecting a stream or beam of electrons through the region parallel to the direction of propagatin of the fast wave, changing the phase velocity of the fast wave `during propagation to a second portion of the region, projecting a stream or beam of electrons through the region parallel to the direction of propagation of the fast wave, changing the phase velcity of the fast wave during propagation to a lower value at the signal frequency in a second portion of the region for exciting a slow wave of signal frequency on the electron stream, directing the signal modulated stream through a third portion of the region for amplifying interaction with the plasma, and then coupling the stream to a fast wave output transmission line in the same manner that the input line is coupled to the stream. The fast wave transmission lines may be coaxial lines or waveguides capable of propagating waves to or near the velocity of light. The pbase velocity of the fast wave on the plasma may be reduced in any suitable manner, as by:

(l) Increasing the density of the plasma in the direction of propagation;

(2) Decreasing the effective capacitance of a dielectric rod forming one boundary for the plasma;

(3) Decreasing the effective inductance of the plasma between the dielectric rod and the conductive boundary;

and

(4) A combination of (1) with (2) or (3).

In the accompanying drawings:

FIG. 1A is an axial section view of a beam-plasma amplifier tube incorporating one embodiment of the present invention;

FIGS. 1B through 1G are graphs showing the variation of plasma frequency, electric field and velocity with distance along the axis of the tube of FIG. 1A;

FIG. 2 is an wdiagram for FIG. 1A;

FIG. 3 is an axial section view of another beam-plasma amplifier tube incorporating another embodiment of the invention;

FIG. 4 is a transverse section view taken on line 4--4 of FIG. 3;

FIG. 5 is an w-diagram for FIG. 3;

FIG. 6 is a fragmentary axial section view of a modiiication of FIG. 3;

FIG. 7 is a transverse section view taken on line 7-7 of FIG. 6; and

FIG. 8 is an ctidiagram for FIG. 6.

The beam-plasma ampliiier tube illustrated in FIG. lA comprises an electron gun 1, a tubular plasma input coupling section 3, a beam-plasma interaction section 5, a tubular plasma output coupling section 7, and a beam collector 9. The tube envelope is made up of a iirst metal section 15 of circular cross section surrounding section 1 and part of section 3, a first tubular wave-permeable window 17, eg., of ceramic, surrounding the rest of section 3, a second tubular metal section 19 surrounding section 5, a second tubular wave-permeable window 21 surrounding part of section 7, and a third metal section 23 of circular cross section surrounding the rest of section 7 and section 9. A tubular metal member 25 and radial metal ring connecting member 27 to section 19 cooperates with the metal section 15 to form an input transition section from a waveguide to a coaxial line, for coupling a signal wave through section 17 to the plasma in section 3. The section is shaped to transform a TMOI wave in the waveguide portion to a TEM wave in the coaxial line portion, as shown by the field arrows in FIG. 1A. A tubular metal member 29 and metal ring member 31 form a similar output transition section with the section 23, for coupling the amplified signal from section 7 to an output waveguide. Members and 27 and section 3 constitute a coaxial input coupler; and section 7 and members 29 and 31 constitute a coaxial output coupler.

A dense plasma is produced in the region made up of sections 3, 5 and 7 by a Penning type discharge between two thermionic cathodes 33 and 35, mounted at the ends of the region, and the intermediate hollow cylindrical metal section 19, which serves as the anode for this discharge. A controlled amount of an alkali metal vapor, such as cesium, for plasma production is provided within the tube, as for example by means of a tubulation 37 connected to a controllable vapor source (not shown). In

operation, a discharge voltage of 4-10 volts is applied between the two cathodes 33, and the anode 19 to produce positive cesium ions and additional electrons in the plasma region by electron-vapor collisions. A strong axial magnetic field is maintained along the length of the tube by a conventional means, such as a solenoid, as indicated by the arrow H, to confine the electrons and ions to substantially axial movement. Moreover, in order to produce a plasma having an extremely high density and percent ionization, the anode 19 may be made of a material, such as tungsten, having an electron work function higher than the ionization potential of the vapor used (eg, 3.9 volts for cesium) in which case the anode should be heated to a temperature sufficient to produce positive ions at the surface -thereof by contact ionization. Cesium plasmas having densities greater than 1014 particles/cm3. at ionization have been produced in this manner.

The plasma density, and hence, the plasma frequency wp along a Penning type discharge, such as that shown in FIG. 1A, varies along the length thereof, being higher near each end near the cathodes 33 and 35 than in the middle along the interaction region 5, as shown by the curve for wp in FIG. 1B. This property of the plasma is utilized in the coupling system shown in FIG. 1A. A cylindrical dielectric rod 39 which is axially mounted in the input coupling section 3, forms the inner boundary of a tubular coupling' plasma. The outer boundary of this coupling plasma is formed by the portion of the metal section 15 extending between the cathode 33 and the window 17. For example, an increase of 160% in plasma density along the tubular plasma results in an increase in wp of about A similar dielectric rod 41 is axially mounted in the output coupling section 7.

A tubular plasma .between dielectric and conductive boundaries supports propagation in a backward wave mode, that is, in a mode wherein the phase and group (energy) velocities are in opposite directions. The transmission line formed by the dielectric rod 39, metal member 15 and plasma therebetween may be termed a tubular plasmaguide.

The electron gun 1 comprises an annular thermionic cathode 43, focusing electrodes 45 and 47, and accelerating electrodes 49 and 51, for projecting a hollow electron beam or stream through the entire plasma region (sections 3, 5 and 7) to the collector 9. The plasma cathodes 33 and 35 may be shielded from the electron gun 1 and collector 9 by apertured discs 55 and 57, respectively. The beam velocity is necessarily only a fraction of the velocity of light, hence it is necessary to greatly reduce the phase velocity of the fast signal wave before coupling to the beam,

As stated above, the input signal wave is converted to a TEM mode wave in the coaxial yline formed by members 15 and 25. This wave is coupled through window 17 to the tubular plasma in section 3 and excites a backward wave therein which propagates toward the plasma cathode 33, toward the left as indicated in FIG. 1A by the broken arrow for its group velocity. The transfer of electrical energy from the coaxial line to the tubular plasma is shown by the electric field curves |E| in FIGS. 1C and 1D. The density of the tubular plasma in the part of section 3 next to the window 17 is adjusted to make the phase velocity vp of the backward wave therein equal to that of waves in the coaxial line (the velocity of light) at the signal frequency at a point such as point A in FIG. 1G at which maximum coupling occurs.

As the backward wave propaga-tes (to the left in FIG. 1A) its phase velocity vp decreases, due to the increase in plasma density and plasma frequency wp described above, as shown by the curve AB in FIG. 1G. Moreover, the backward wave is converted during such propagation from a wave having predominantly transverse electric fields to a wave having substantial longitudinal fields, as shown by the electric field arrows in FIG. 1A. The velocity of the electron beam is adjusted to synchronize with the reduced forward phase velocity of the backward wave at a point B in section 3, in order that the backward wave will excite a forward signal wave on the beam. This coupling is indicated in FIG. 1A by the bracketed solid arrows for the phase velocities of the two waves in section 3. The transfer of energy from the plasma wave to the beam wave is shown in FIGS. 1D and 1E.

After being thus signal modulated the forward wave on the beam propagates to and through the interaction section 5 in which it interacts with a space charge wave in the solid plasma therein to amplify the signal.

FIG. 2 is an w-,B diagram, which is a conventional means for graphically showing the wave propagating characteristics of wave propagating media such as transmission lines, electron streams and plasmas. Since w is the angular velocity and ,8 is the phase shift per unit length along the medium, each point on the graph represent a particular phase velocity as determined by the ratio w/ [8 at that point, and each straight line through the origin represents the locus of points .of equal phase velocity. In FIG. 2, the curve labeled PSW1, is the wave propagating characteristic for surface waves on the tubular plasma in the -first part of coupling section 3, for an example in which quartz is used for the dielectric rod 39. As shown, this curve intersects the characteristic for waves in the coaxial line at point A, corresponding to point A in FIG. 1G. This means that a signal of frequency ws in the coaxial line will induce or ex-cite a PSWI wave of the same frequency on the tubular plasma. Curve PSW2 is the wave characteristic for the same surface wave after propagation to the higher density portion of section 3 to point B of FIG. 1B. The beam velocity vb (and the group velocity of waves on the beam) is shown by the dashed line, and the wave characteristic of slow space charge waves on the beam is shown by the curve labeled SSCW. This curve is substantially straight and parallel to the beam velocity line, except near the origin as shown. The extension of the straight portion intersects the -w axis at -wpB, the plasma frequency of the beam. The beam velocity is adjusted to make the SSCW curve intersect the PSWZ curve at ws, at point B in FIG. 2, in order to couple the signal wave PSW2 on the tubular plasma to the forward wave SSCW on the beam at signal frequency.

The plasma frequency wp1 of the tubular plasma at point A (FIG. 1G) is shown in FIG. 1B to be a little higher than the signal frequency ws. However, in the interaction section 5 the plasma frequency wp3 of the solid plasma is substantially equal to ws. Thus, the modulated beam interacts with a space charge wave in the solid plasma at that frequency. The plasma frequency w2 of the decelerated waves PSWZ (the intersection of curve PSW2 with the w-axis) is too high to be shown on FIG. 2. The wave characteristic of the plasma space charge wave is the solid horizontal line, labeled PSCW, through ws,

A and B, in FIG. 2. Coupling between the modulated beam wave SSCW and plasma wave PSCW occurs at point C in FIG. 2 and begins near point C in FIGS. 1E and 1F, which show the growth or amplification of the electric field [El in the electron beam and the plasma, respectively. Points B and C indicate RF coupling in two separate regions in FIGS. 1G and 1F, although they are superimposed at the same velocity point in FIG. 2tl

After being amplified in passing through the interaction section 5, the signal wave on the beam is coupled in output section 7 to a slow plasma surface wave, which in turn is accelerated and coupled to a fast wave in the output line, in exactly the same manner as in the input coupling system, except in reverse.

Instead of utilizing only changes in plasma density to change the phase velocity of the coupling waves, other properties of the structure may be varied, alone or in combination with changes in plasma density for this purpose. Also, other types of input transmission lines can be used. FIGS. 3 and 4 show an embodiment in which hollow wave guides are coupled to tubular plasmaguides, the wave propagating characteristics of which are varied by varying the structure of the dielectric rods. The tube comprises a sealed envelope 61, e.g., of glass, containing an electron gun 63, a tubular plasma input coupling section 65, a beam-plasma interaction section 67, a tubular plasma output coupling section 69 and a collector 71. The three plasma sections 65, 67 and 69 comprise a hollow cylindrical metal anode member 73, annular plasma cathodes 75 and 77 at the ends of member 73, a dielectric rod 79 in coupling section 65, and a dielectric rod 81 in coupling section `69. Cesium vapor is supplied to the space within anode 73 through a tubing 83 connected to a generally U-shaped by-pass tubing 85 containing liquid Cesium 87. The cesium reservoir is heated, as by a coil or tape 89, to maintain a vapor pressure of 10-2 to 1 torr in the anode. A water jacket may be provided at 91 to control the cesium condensation. A cold trap 93 may be provided between the electron gun 63- and the rest of the tube to maintain a lower pressure in the gun region.

The density of the tubular plasma in the coupling section 65 increases in the direction from the interaction region toward the plasma cathode 75, as in FIG. 1A. Moreover, in order to produce a greater change in phase velocity of waves on the plasma, the dimensions of the dielectric rod 79 are varied while maintaining the internal diameter c of anode 73 constant. The rod 79 has a uniform external diameter and is made up of a solid first portion 95 at the end adjacent the interaction section 67, a tapered internal diameter section portion 97 and a thinawalled hollow portion 99 connected to the solid first portion 95 by the tapered second portion 97. The dielectric rod constitutes a distributed capacitance forming part of the transmission line. Since v=w/ and 1 ...t/ro

for backward waves, the decrease in capacitance from section 95 to section 99 produces a decrease in phase velocity of waves propagated along the line, which adds to the decrease in phase velocity due to the increase in plasma density.

The input RF signal to be amplified is introduced to the tube through a generally rectangular hollow input waveguide section 101 having its end portion parallel to the input tubular plasmaguide 65 and coupled through apertures 103 in the anode 73 to the first portion of the plasma. guide, viz. the part including the solid dielectric portion 95. The coupling operation for an example in which the dielectric rod 79 is of ceramic is illustrated by the wdiagram of FIG. 5. The characteristic curve for the input waveguide 101 is a parabola crossing the w-axis at wo, the cutoff frequency, and merging at high frequencies with the dashed line showing the velocity of light. At the signal or operating frequency of the tube, the phase velocity in the waveguide is somewhat higher than the Velocity of light, at point A. In order to couple input waves of frequency ws to the plasmaguide coupler 65, the density of the plasma in the first portion of the coupler is adjusted to make the characteristic curve PSWl of the backward waves intersect the waveguide curve at ws, or point A, as in FIG. 2. If the plasma density (and wp) were constant throughout the tubular plasmaguide coupler, the effect of the change in dielectric material between portions and 99 would be to shift the PSW1 curve to the right, as shown by the dashed curve PSW2 in FIG. 5, which intersects the horizontal Ws line at point B1, and shows the wave characteristic for the condition where b/a is nearly unity in FIG. 4. However, since the plasma density (and wp) also varies, the net effect of the two variations is curve PSW3, the characteristic of backward surface waves in the third portion of the coupler, which curve intersects the ws line at point B2. The beam velocity is adjusted to couple the backward wave PSW2 to a slow space charge wave SSCW on the beam at the signal frequency ws, at point B2. As shown, the lbeam velocity required is considerably below that required for coupling at point B1. After being modulated by the input signal, the beam wave SSCW interacts with the solid plasma in interaction section `67 as in FIGS. 1 and 2. Preferably, additional plasma cathodes and 107 are provided, at the ends of dielectric rods 79 and 81, to maintain uniform plasma density in section 67. As in FIG. l, the anode is preferably made of a high work function metal and is heated to produce additional Cesium ions by contact ionization. After amplification, the RF signal on the beam is coupled to a backward surface wave in the output plasmaguide section 69, which wave is accelerated and coupled through apertures 109 in anode 73 to an output waveguide section 111.

FIGS. 6 and 7 show a modification of FIG. 3 in which the dielectric rod 79 is solid throughout its length (e120) and the diameter of the surrounding conducting surface varies between c1 to c2 at the ends of the rod 79'. Thus, the anode 73 comprises a first section 113 of large diameter, a tapered second section 115, and a third section 117 of smaller diameter. The effect of the reduction in diameter is to reduce the thickness of the tubular plasma, which reduces the distributed inductance contributed by the plasma to the transmission line and thereby reduces the phase velocity of the backward waves on the tubular plasma. The effect of this reduction in phase velocity without any change in plasma density is shown by the dashed curve PSWZ in FIG. 8, where PSW1 is the characteristic curve for backward waves in the -first section 113'. The net effect of the reduction in plasma thickness and the increase in plasma density along the tubular plasmaguide is shown by the curve PSW3 for backward waves in section 117. Comparison of FIG. 8 with FIG. 5 shows that the plasma thickness variation is more effective than the -dielectric material variation. The remainder of the operation is the same as described for FIGS. 3 to 5.

It will be understood that FIGS. 3 and 6 could be combined, by using the variable dielectric rod of FIG. 3 with the variable anode diameter of FIG. 6, to reduce the phase velocity still further. Moreover, the change in plasma density may be increased in any of FIGS. 1, 3 and 6 by dividing the outer conductive wall of each tubular plasmaguide into at least two insulated sections and applying different DC potentials thereto. If the section nearest the cathode is biased more positive than the other section (nearest interaction region), ions will fiow to the other section and reduce the overall plasma density in that region with respect to the plasma-density in the cathode section.

What is claimed is:

1. Means for coupling a fast wave transmission line to a plasma at a given frequency, comprising:

(a) means for producing a plasma in a given region;

(b) means for coupling a fast wave transmisison line to the plasma in a first portion of said region to excite a fast backward wave at said frequency on said plasma for propagation to a second portion of said region; and

(c) means for changing the phase velocity of said fast backward wave during said propagation to a different value at the some frequency in said second portion.

2. Means for coupling a fast wave transmission line to an electron stream at a given frequency, comprising:

(a) means for producing a plasma in a given region;

(b) means for coupling a fast wave transmission line to the plasma in a first portion of said region to excite a fast backward wave at said frequency on said plasma for propagation to a second portion of said region;

(c) means for projecting a stream of electrons through said region in a direction opposite to the direction of propagation of said fast backward wave; and

(d) means for changing the phase velocity of said fast backward wave during said propagation to a lower value at the same frequency in said second portion, for exciting a slow forward wave of said lower phase velocity at said frequency on said electron stream.

3. Means for coupling a fast wave transmission line to a plasma at a given frequency, comprising:

(a) means for producing a plasma in a given region;

(b) means for coupling a fast wave transmission line to the plasma in a first portion of said region to excite a fast backward surface `wave having predominantly transverse electric fields at said frequency on said plasma for propagation to a second portion of said region; and

(c) means for converting said fast backward surface wave during said propagation to a similar wave having substantial longitudinal electric fields at said frequency in said second portion.

4. Means for coupling a fast wave transmission line to an electron stream at a given frequency, comprising:

(a) means for producing a plasma in a given region;

(b) means for coupling a fast wave transmission line to the plasma in a first portion of said region to excite a fast ybackward wave having predominantly transverse electric fields at said frequency on said plasma for propagation to a second portion of said region;

(c) means for projecting a stream of electrons through said region in a direction parallel to the direction of propagation of said fast backward wave; and

k(d) means for converting said fast backward wave during said propagation to a backward wave having a lower phase velocity and substantial lon-gitudinal electric fields at the same frequency in said second portion, for exciting a slow space charge wave of said lower phase velocity having substantial longitudinal electric fields at said frequency on said electron stream.

5. Means for coupling a fast wave transmission line to a plasma at a given frequency, comprising:

(a) a hollow conductive member;

(b) an elongated dielectric member coaxially disposed within said hollow member;

(c) means for producing a plasma in the space between said members;

(d) means for coupling a fast wave transmission line to the plasma in a first portion of said space to excite .a fast backward wave of given frequency on said plasma for propagation to a second portion of said space; and,

(e) means for changing the phase velocity of said backward wave during said propagation to a different value at the same frequency in said second portion.

6. Means for couplin-g a fast wave transmission line to an electron stream at a given frequency, comprising:

(a) a hollow conductive means;

(b) an elongated dielectric means coaxially disposed within said hollow means;

(c) means for producing a plasma in the space between said conductive and dielectric means;

(d) means for coupling a fast wave transmission line to the plasma in a first portion of said space to excite a fast backward wave of given frequency on said plasma for propagation to .a second portion of said space;

(e) means for projecting a stream of electrons through said space in a direction opposite to said backward wave; and

(f) means for changing the phase velocity of said backward wave during said propagation to a lower value at the same frequency in said second portion for exciting a slow space charge wave of said lower phase velocity at said frequency on said electron stream.

7. Coupling means as in claim `t5, wherein said hollow means is a cylindrical member, and said dielectric means comprises a solid portion extending along said first portion, a thin hollow portion extending along said second portion, and a hollow transition portion of tapered internal diameter connecting said solid and hollow portions.

8. Coupling means as in claim 6, wherein said dielectric means is a cylindrical member, and said hollow means comprises a cylindrical portion of given diameter extend ing along said first portion, a cylindrical portion of smaller diameter extending along said second portion, and a transition portion of tapered diameter connecting said cylindrical portions.

9. Coupling means as in claim 6, wherein said lastnamed means comprises means for establishing an increasing plasma density gradient between said first portion and said second portion.

10. A beam-plasma interaction tube comprising:

(a) means for producing a plasma in a given region;

(b) means for coupling a fast wave transmission line to the plasma in a first portion of said region to excite a fast backward wave at said frequency on said plasma for propagation to a second portion of said region;

(c) means for projecting a stream of electrons through said region in a direction parallel to the direction of propagation of said fast backward wave;

(d) means for changing the phase velocity of said fast backward wave during said propagation to a lower value at the same frequency in said second portion, for exciting a slow forward wave of said low phase velocity at said frequency on said electron stream;

(e) means for directing said electron stream from said second portion to a third portion of said region, for interaction with the plasma therein to increase the amplitude of said slow forward wave; and

(f) means for coupling said amplified slow forward wave to a fast wave transmission line.

References Cited UNITED STATES PATENTS 11/1963 Agdur 315--39 6/ 1966 Roberts B15-3.5 8/1966 Ayaki S15-3.5 5/1967 Ferrari 330-41 X OTHER REFERENCES HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner.

S. CHATMON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,37B ,723 April 16 1968 Louis S. Napoli et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, lines 14 to 17, cancel "to a second portion of the region, projecting a stream or beam of electrons through the region parallel to the direction of propagation of the fast wave, changing the phase velcity of the fast Wave during propagation"; line 26, "to" should read at Column 5, line 7, after "1F," insert respectively, line SO, "section" should read second Column 7, line 8, "some" Should read same Signed and sealed this 14th day of October 1969. (SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E.

Attesting Officer Commissioner of Patents 

1. MEANS FOR COUPLING A FAST WAVE TRANSMISSION LINE TO A PLASMA AT A GIVEN FREQUENCY, COMPRISING: (A) MEANS FOR PRODUCING A PLASMA IN A GIVEN REGION; (B) MEANS FOR COUPLING A FAST WAVE TRANSMISSION LINE TO THE PLASMA IN A FIRST PORTION OF SAID REGION TO EXCITE A FAST BACKWARD WAVE AT SAID FREQUENCY ON SAID PLASMA FOR PROPAGATION TO A SECOND PORTION OF SAID REGION; AND (C) MEANS FOR CHANGING THE PHASE VELOCITY OF SAID FAST BACKWARD WAVE DURING SAID PROPAGATION TO A DIFFERENT VALUE AT THE SOME FREQUENCY IN SAID SECOND PORTION.
 10. A BEAM-PLASMA INTERACTION TUBE COMPRISING: (A) MEANS FOR PRODUCING A PLASMA IN A GIVEN REGION; (B) MEANS FOR COUPLING A FAST WAVE TRANSMISSION LINE TO THE PLASMA IN A FIRST PORTION OF SAID REGION TO EXCITE A FAST BACKWARD WAVE AT SAID FREQUENCY ON SAID PLASMA FOR PROPAGATION TO A SECOND PORTION OF SAID REGION; (C) MEANS FOR PROJECTING A STREAM OF ELECTRONS THROUGH SAID REGION IN A DIRECTION PARALLEL TO THE DIRECTION OF PROPAGATION OF SAID FAST BACKWARD WAVE; (D) MEANS FOR CHANGING THE PHASE VEOCITY OF SAID FAST BACKWARD WAVE DURING SAID PROPAGATION TO A LOWER VALUE AT THE SAME FREQUENCY IN SAID SECOND PORTION, FOR EXCITING A SLOW FORWARD WAVE OF SAID LOW PHASE VELOCITY AT SAID FREQUENCY ON SAID ELECTRON STREAM; (E) MEANS FOR DIRECTING SAID ELECTRON STREAM FROM SAID SECOND PORTION TO A THIRD PORTION OF SAID REGION, FOR INTERACTION WITH THE PLASMA THEREIN TO INCREASE THE AMPLITUDE OF SAID SLOW FORWARD WAVE; AND (F) MEANS FOR COUPLING SAID AMPLIFIED SLOW FORWARD WAVE TO A FAST WAVE TRANSMISSION LINE. 